N. Korea May Have Doubled its Nuclear Weapons Cache

North Korea may have doubled its nuclear weapons stockpile over the past year and a half.

That's according to the Washington-based Institute for Science and International Security, which estimated that North Korea may have added six or more weapons after expanding its production of weapons-grade uranium and plutonium, the London Daily Mirror reported.

The report came just a week after Reuters quoted a State Department official saying North Korea had begun producing plutonium fuel again, an indication it planned to pursue its nuclear weapons program despite international sanctions following its fourth nuclear test last January.

The report was based in part on satellite imagery of the site.

At the end of 2014, North Korea was thought to have between 10 and 16 nuclear weapons.

In 2013, North Korea announced it was restarting its main reactor and a smaller plant. That plant was shut down in 2007 in compliance with an international agreement for aid in exchange for disarmament, which fell apart.

Last month, Kim Jong-un said he would build up the country's nuclear weapons capability.